The reprocessing and subsequent utilization of thermoplastic material has been of increasing importance and reprocessing methods and apparatus for producing polymers of thermoplastic condensate are known in the art.
It has been previously found that there is a problem with regard to sufficient removal of low molecular substances, particularly water, from the polymer in order to prevent material decomposition and thus to produce a satisfactory polymer product with sufficient final viscosity.
Attempts have been made to remove the moisture of recondensation deposited on the surface as well as the interior of the thermoplastic materials by a preliminary drying operation. However, this requires considerable time.
DE 29 42 248 discloses a reprocessing method in which finely shredded fibers of polyethylene terephthalate are initially compacted in a screw press and the compressed fibers are introduced into a dual screw extruder to remove additional water and volatile impurities from a melt of the fibers in the extruder. After filtration of the product it is recondensed in an autoclave under reduced pressure to increase its viscosity without addition of new polymer.
The pressure buildup necessary in this relatively expensive process for repeated product delivery leads to an undesirable molecular decomposition. In addition the energy losses over a relatively long processing time are considerable.
DE 21 28 468 discloses a batch mixer having spiral blades which rotate opposite one another in a hopper-shaped tank for the final processing in a condensation polymerization. The batchwise treatment does not produce a satisfactory grade of the polymer since a sufficient breakdown of the polymer mass is not produced in the small volume of the mixer.